DerGut commented on code in PR #3000:
URL: https://github.com/apache/iceberg-rust/pull/3000#discussion_r3842573671


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crates/integrations/datafusion/src/catalog_access.rs:
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@@ -0,0 +1,192 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use std::collections::HashMap;
+use std::sync::Arc;
+
+use async_trait::async_trait;
+use datafusion::catalog::Session;
+use datafusion::error::Result as DFResult;
+use iceberg::table::Table;
+use iceberg::{
+    Catalog, Namespace, NamespaceIdent, Result, SessionCatalog, 
SessionContext, TableCommit,
+    TableCreation, TableIdent,
+};
+
+use crate::SessionContextResolver;
+
+/// Describes how the DataFusion integration accesses an Iceberg catalog.
+///
+/// A catalog can either be accessed directly through [`Catalog`] or through a
+/// [`SessionCatalog`] bound to an Iceberg [`SessionContext`]. Operations that
+/// receive a DataFusion session resolve and bind its context once. Operations
+/// for which DataFusion provides no session reuse one anonymous fallback
+/// context so session-scoped catalog state remains stable across those calls.
+#[derive(Clone, Debug)]
+pub(crate) enum CatalogAccess {
+    /// A catalog accessed directly through the [`Catalog`] API.
+    Direct(Arc<dyn Catalog>),
+
+    /// A session-aware catalog, its resolver, and the stable context used by
+    /// DataFusion APIs that do not expose a session.
+    SessionAware {
+        catalog: Arc<dyn SessionCatalog>,
+        resolver: Arc<dyn SessionContextResolver>,
+        fallback_context: SessionContext,
+    },
+}
+
+impl CatalogAccess {
+    pub(crate) fn with_session(&self, session: &dyn Session) -> 
DFResult<Arc<dyn Catalog>> {

Review Comment:
   I've replaced the `CatalogAccess` with a `SessionBindingCatalogAdapter` 
(renamed from `SessionBoundCatalog` to mirror the reverse 
`SessionDroppingCatalogAdapter`) in 
https://github.com/apache/iceberg-rust/pull/3000/changes/5eecdff089b53aceae0ba9cd738effee609064cd.
   
   Together with the dropping of the `SessionContextResolver` trait (in 
https://github.com/apache/iceberg-rust/pull/3000/changes/fc3995bb95d7f8e6249c5e5cbba712920559009b),
 a `DataFusionCatalog` isn't required any more to encapsulate both pieces.
   
   At the same time, the `SessionBindingCatalogAdapter` now double-acts as the 
`dyn SessionCatalog` to power session-aware operations during scan and insert 
planning, as well as the `dyn Catalog` to power session-unaware operations, and 
bridge to Catalog-based APIs such as the 
[`IcebergCommitExec`](https://github.com/DerGut/iceberg-rust/blob/5eecdff089b53aceae0ba9cd738effee609064cd/crates/integrations/datafusion/src/physical_plan/commit.rs#L43)
 or 
[`Transaction::commit`](https://github.com/DerGut/iceberg-rust/blob/2ec44f15226c46f389ab341e451e25cdfcb2bc9a/crates/iceberg/src/transaction/mod.rs#L175).
 As a consequence, it is now harder to introduce it in a follow-up PR, and I 
need to rethink how to best break this change down into two or more pieces.



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